Which of these is a positive check according to Malthus?

In Malthusian theory, a positive check refers to factors that increase the death rate in a population, thus helping to control population growth. War is typically seen as a classic example of a positive check because it can lead to significant loss of life, thereby reducing the overall population size. In Malthus's viewpoint, when a population exceeds the carrying capacity of its environment, checks like war can act to restore balance by decreasing population numbers through mortality.

Conversely, the other options listed—late marriage, celibacy, and moral restraint—are considered preventive checks in Malthusian theory. These factors act to lower the birth rate by influencing personal choices regarding reproduction before birth occurs rather than directly reducing population through mortality. Therefore, the correct identification of war as a positive check is consistent with Malthus's classification of factors that directly contribute to increased mortality within a population.